Electrolyte manganese dioxide (EMD) can be presently produced by using titanium, lead or graphite as the anode for an electrolyte of a manganese sulfate solution. Preferably, the use of a titanium anode has been used to obtain good electrolytic manganese dioxide. When using the titanium anode, the upper limit of the current density has been found to be 0.8 to 1.0 ampere per square centimeter. If the current density exceed this limit, it has been observed that a passive film is formed on the titanium electrode and the voltage of the electrolytic cell increases rapidly so that the electrolysis can not continuously be performed. To overcome the passavation of the titanium electrode and the associated voltage increase, it has been proposed in Japanese patents Kokai Sho 47-42711 and Kokai Sho 61-47911 to use suspension of EMD, or acetylene or carbon black powders, respectively, in the electrolytic bath. This process is called a slurry bath.
In the operation of the slurry process, making a stable carbon powder suspension in the electrolyte is difficult since the carbon particles, such as acetylene black, are hydrophobic and therefore are difficult to wet.
It is an object of the present invention to effectively eliminate the difficulty of making a good suspension of carbon particles in an electrolytic bath by the method of sulfonizing the surface of the carbon particles prior to their being fed into the electrolytic bath. Various carbon particles are suitable for use in this invention such as acetylene black, carbon black, and the like. However, the preferred carbon particles are acetylene black.
The sulfonation of the surface of carbon particles can be accomplished by mixing carbon particles, such as acetylene black, and fumic sulfuric acid. The temperature of the mixture will rise (generally to about 70.degree. C.) due to its exothermic reaction. After standing for a suitable period, for example over night, the mixture cools to room temperature. The carbon particles are then separated by filtration and the surface of such particles will be sulfonized. The sulfonated carbon particles are easily dispersed in the electrolyte of the ENID production bath and EMD can be readily produced. The EMD produced using the sulfonated carbon particles have been found to contain some carbon and have a good discharge capability while also being easy to grind. Therefore the production method of this invention is better than the existing processes since it produces electrolytic manganese dioxide that has good discharge capability, good grinding characteristics and can produced EMD in the process at higher current density, for example up to three times greater current density than the conventional process.